1. Field
The disclosure relates to envelope tracking for power amplifiers.
2. Background
Envelope tracking is a technique for increasing the efficiency of power amplifiers. In an envelope tracking (ET) system, the supply voltage of a power amplifier is dynamically adjusted to keep the power amplifier operating with sufficient headroom to maintain linearity, while nevertheless minimizing DC power consumption. The supply voltage of the power amplifier may be generated using a separate linear amplifier that tracks the envelope of the power amplifier output. In certain implementations, the linear amplifier is itself coupled to an amplifier supply voltage generated by a boost converter, which is capable of generating a boosted supply voltage for the linear amplifier that exceeds the maximum supply voltage otherwise available to the system, e.g., a battery voltage. In this manner, the power amplifier output can reach and even exceed the battery voltage when necessary.
To increase efficiency, the boost converter may generate a boosted supply voltage for the linear amplifier only when necessary to provide sufficient headroom to the power amplifier. When the boost converter is not turned on, a bypass mode may be provided in which the battery voltage is directly coupled to the amplifier as the amplifier supply voltage.
In view of the desire to provide improved efficiency for ET systems, it would be desirable to provide techniques for determining when to enable a boost converter to generate the boosted supply voltage, and further for determining the target voltage to which the boosted supply voltage should be driven when the boost converter is enabled.